1. Field of the Invention
The present invention relates to the field of fan drive devices, and particularly to a multi-speed fan drive.
2. Description of the Prior Art
Devices for fan drives are well known in the prior art, and typically have included a one-speed direct drive coupling or a variable-speed fluid shear coupling mechanism. The purpose of the viscous fluid couplings of the prior art typically has been to provide for variable speed driving of the fan depending upon a monitored speed or temperature.
In U.S. Pat. No. 4,064,980, issued to Tinholt on Dec. 27, 1977, there is disclosed a dual speed viscous fluid coupling. The Tinholt device includes an output member defining two fluid chambers and an input member disposed in each of the fluid chambers. The input members are driven at two different rotational speeds. The dual speeds for the coupling are provided by selectively pumping a viscous fluid into one or the other of the fluid chambers to derive the speed associated with the input member within the respective chamber. Another multi-speed fan drive is disclosed in U.S. Pat. No. 3,972,399, issued to Bopp on Aug. 3, 1976. The Bopp device includes a viscous fluid working chamber and a temperature control which operates to vary the volume of fluid within the chamber to derive differing speeds in response to temperature changes. Another version of a temperature sensitive coupling for fan drives is shown in U.S. Pat. No. 4,036,339 issued to Kikuchi on July 19, 1977. The Kikuchi device uses a magnetic force to overcome a spring force below a selected temperature to provide a first drive speed. At higher temperatures, the magnetic attraction is lower than the spring force and fluid is transferred into the working chamber to provide a second speed for the fan.
It is desirable that a multi-speed fan drive provide fan speeds which are within desired ranges. It is also preferable that the fan drive have a minimum amount of frictional or other losses associated with the driving action. The prior art multi-speed devices have generally been associated with fluid shear drives which by the nature of the fluid shear action have frictional losses and inefficiencies associated with them. In contrast to the prior art, it is a particular advantage of the present invention that a multi-speed fan drive is provided which includes a direct drive of the fan at the differing speeds to minimize these losses and inefficiencies, and also to positively control the desired minimum to maximum fan speed range.
The use of planetary gear assemblies is well known in transmission systems. In U.S. Pat. No. 3,532,008, issued to Fanstone on Oct. 6, 1970, there is disclosed a planetary transmission with slip couplings. The Fanstone device directly relates to outboard motor transmission systems, and discloses in FIGS. 12 and 13 a typical planetary gear arrangement. In certain instances, the planetary gear transmissions have included over-running or one-way clutches. Examples of such transmission systems are shown in U.S. Pat. No. 2,945,570, issued to Ferguson et al. on July 19, 1960 and U.S. Pat. No. 2,266,740, issued to Cotterman on Dec. 23, 1941. A further example of an over-running clutch is shown in U.S. Pat. No. 4,046,239, issued to Tinholt on Sept. 6, 1977.